What is Spin: Definition and 1000 Discussions

Homework Statement a) If a spin-1/2 particle is in the up spin state along z, what is the probability that if its spin along the y-direction is measured it will be found to be pointing in the “up” direction along y? (b) Calculate the expectation values of the components of S, i.e. {Sx, Sy...

Homework Statement I am currently working on a seemingly straightforward eigenvalue problem appearing as problem 1.8 in Sakurai's Modern QM. He asks us to find an eigenket \vert\vec S\cdot\hat n;+\rangle with \vec S\cdot\hat n\vert\vec S\cdot\hat n;+\rangle = \frac\hbar 2\vert\vec S\cdot\hat...

Does spin up mean which way the magnetic field is pointed in relation it's environment (so when do you know if it is up or down, or does that depend on the enviroment?) So if it is spin up, it means the field lines go from up to down, and vice versa. So spin pretty much means where the poles...

So, my current understanding of spin is that when particles with a certain spin state hit a stern gerlach device, their wavefunction is split into components, deflection associated with one of the pure spin states aligned with the device. For spin 1/2 particles, there are only supposed to be two...

I was trying to understand the QM tests done to show the violation of Bell’s inequality. In the example given this was done by testing the polarization of entangled photons which were positively correlated. So in the example Alice and Bob are detecting the polarisation for the two entangled...

Hey guys I was wondering what would happen if: took a ball neo magnet, balanced it on a few other magnets to basically make it a frictionless bearing. Then spin the ball magnet to 10k rpm. But do all this in a box that's a vacuum. Would the neo ball magnet spin basically for a VERY long...

What subatomic particle is emitted when a diatomic Hydrogen molecule transitions from Orthohydrogen to Parahydrogen? e.g. during cooling And why can you cool a sample of Hydrogen to assure that all H2 molecules are para-, but you cannot heat to have any more than 3:1 ortho-:para- ?

Can you have a left handed pion? i.e. it's spin is opposite to its direction of flight

Homework Statement I have a B field initially in the x-direction, and its constant: \widehat{H}= - (\dfrac{e}{mc})\overrightarrow{B} \dot{} \overrightarrow{S} At t=0 it was prepared so that Sz has an eigenvalue of + hbar/2 I want to show the time evolution of the initial state. Homework...

Hi folks, I work in theoretical high energy physics. Recently I got interested in condensed matter theory. But each time I see some spin system I get scared thinking another one must be waiting for me! Can some one suggest me some reference(s) where these spin chains, specially those which are...

As I understand it, there is a certain probability associated with detecting spin states. Which if the spin state is unknown prior to testing is 0.5. But if I prepare an electron with say spin up, then measure it again for spin up I will detected spin up 100% of the time. Also, if I prepare...

Homework Statement [/B] Just trying to find the spin 3/2 rotation matrix, I've found spin 1/2 and spin 1. This isn't a homework problem just studying some other spins. Homework Equations For spin 1/2: Rn(Φ) = cos(Φ/2)1ˆ − isin(Φ/2)σn For spin 1: Un(Φ) = e −iΦSn = 1ˆ − isin(Φ) · Sn − (1ˆ −...

I just want to clear up something about electron spin to see if I have it correctly. As far as I understand it is it not really spinning but it's just a convenient word and what it denotes is the the particular quantum number is either up or down. Now I think I've got it right to say that this...

Homework Statement Spin can be represented by matrices. For example, a spin half particle can be described by the following Pauli spin matrices s_x = \frac{\hbar} {2} \begin{pmatrix} 0 & 1 \\ 1 & 0 \end{pmatrix} , s_y = \frac{\hbar} {2} \begin{pmatrix} 0 & -i \\ i & 0 \end{pmatrix} , s_z =...

Hey I'm curious if it would be possible to measure if a particle's spin is in a superstate similar to how the double slit experiment can show whether or not an electron's location is in a superstate. Wouldn't such a machine allow for FTL communications, since if we measure one of two entangled...

how fast does an electron spin? if an electron has no volume and is a point, then surly speed would have no meaning. So could it spin at what ever speed it likes? would it just be pure spin (think of a square, it has 4 corners and 4 sides, if the length of the sides were zero, then it would be...

ok i just learned that spin comes up when l (azimuthal quantum number) is half integer but then my book says that each elementary particle has a specific and immutable value of spin. Ok now does this mean that l (azimuth quantum number) takes two values at once - One value corresponding to spin...

When trying to solve ##\mathbb{S}^2 =\hbar^2s(s+1)\mathbb{I},## I got that ##\mathbb{S}^2 = \mathbb{S}^2 _x+\mathbb{S}^2_y+\mathbb{S}^2_z = \frac{3\hbar^2}{4} \left[\begin{array}{ c c }1 & 0\\0 & 1\end{array} \right] = \frac{3\hbar^2}{4}\mathbb{I},## but how does ##\frac{3\hbar^2}{4} =...

Homework Statement On an ice rink two skaters of equal mass grab hands and spin in a mutual circle once every 2.5s. If we assume their arms are each 0.80m long and their individual masses are 55.0kg , how hard are they pulling on one another? Homework Equations ## a_c = \frac {v^2}{R} ## ## v...

Spin or angular momentum in my book is formulated in the basis of eigenstates of the operator that measures the angular momentum along the z-axis. But in principle I guess this could just as well have been done in the basis of eigenstates of Ly or Lx. Will that change anything in the equations...

Homework Statement An ion has effective spin ħ. The spin interacts with a surrounding lattice so that: Hspin = A S2 z. I first had to write H as a matrix. Then i had to find the energy eigenvalues. Homework EquationsThe Attempt at a Solution I figured j=1 and mj = 1,0,-1 S2 z = ħ2(1 0 0; 0...

Things I don't understand: What do they mean by "two spin-1/2 doublets and a spin-3/2 quadruplet"? Why do they use the two flavours "+2/3e and -1/3e" ?

In 4-D Hilbert space for 2 electrons is |up1>|down2> equivalent to |down1>|up2> due to electrons being identical ?

I was trying to calculate the ##^{19}_{9}F_{10}## nuclear spin using the nuclear shell method. From what i know the nuclear spin for a nucleous with odd ##A## is the total angular momentum ##J## of the stand-alone nucleon: P: ##(1d_{5 \backslash 2})^1## (stand-alone nucleon) N: ##(1d_{5...

Are there any elementary particles with zero intrinsic spin? Thanks in advance.

Hey guys, I'm very new to quantum mechanics and have purchased 'Quantum Mechanics: The Theoretical Minimum. I'm still a bit confused by a fairly fundamental idea. In the book, it states that you first prepare a spin state (say the σz = +1) in the initial measurement. If you rotate the...

1. Problem: Consider the composed system of two particles of spin ##s=1## where their angular momenta is ##l=0##. What values can the total spin take if they identical? What changes when they are distinguishable? The Attempt at a Solution : The problem I have here is incorporating the fact...

A simple question: If we have $$z$$ is a complex function, and we have here $$\omega_\mu^{ij}$$ represents some spin connection where $$\mu$$ is spacetime corrdinate. And say we have $$z + \omega_\mu^{12}$$ no matter for now what the metric is, if I want to take the conjugate of this, is the...

Homework Statement Two particles with spin ##S_1=1## and ##S_2=1## are in our system. For wavefunction of the first particle we know that ##S_{1z}|\psi _1>=\hbar |\psi _1>## while for the second particle ##S_{2x}|\psi _2>=\hbar |\psi _2>##. a) Find wavefunction ##|\psi _1>## in basis with...

1. In Griffiths, in the section where he discusses the 'total' spin of two spin 1/2 particles (''Addition of angular momenta'') he starts of using a notation new to me. Namely ##\chi=\chi_1\chi_2## where I know what ##\chi_1## and ##\chi_2## represent independently, which has been discussed in...

In texts about quantum computing, one prepares electrons or other particles in definite spins (up or down), then pass them through various gates, etc. But since the probability that an electron changes spin state within a very short time, then how can this be realistically done? Is there a way...

Let us suppose that a cylindrical bottle is on the surface of the water (filled with air for simplicity). A little spin is given to the bottle makes it rotating around the symmetry axis of the cylinder. After a while the bottle stops rotating. How to calculate the time duration of spinning?

Could you please put the conclusion ("The spin-statistics theorem says that in local quantum field theory in two dimensions an anticommuting field must have half-integral Lorentz quantum numbers.") of the following quote in simpler terms if possible, "Properly speaking, in 1+1 dimensions there...

In my quantum mechanical studies, I came across the information that if you know an electron's spin on one axis, then you can not know its spin on another axis. For example, if you know that an electron is spin up on the z-axis, then apparently due to the Uncertainty Principle, you can not know...

In The Theoritical Minimum we shown all spins states use just two states up and down. How can we do that.? I am confused about the directions of states and normal coordinate system Can somebody help me ? Thanks

The Dirac equation in 3+1 space-time yields spin, is this still true in 1+1d space-time? If not what do the 2 components of the spinor represent? Do we still have intrinsic spin in 1+1d space-time? Thanks for any help!

I am reading a book The Theoretical Minimum I didnt understand spin and quantum states "All possible spin states can be represented in a two dimensional vector space." What it means ?

Homework Statement (a) The nitrogen atom has seven electrons. Write down the electronic configuration in the ground state, and the values of parity (Π), spin (S), orbital angular momentum (L), and total angular momentum (J) of the atom. (b) If an extra electron is attached to form the N–...

For an electron the spin operator S_zis represented by a 2×2 matrix, with spin up and down as its bases. Consider the angular momentum operator L_z with l=1 which is a 3×3 matrix. How can we treat the L_z S_z operator directly in matrix form?

I've been watching Leonard Susskind's videos on quantum entanglements. Naturally, one of the things that he has been discussing is spin and its various operator Hermitian matrices and eigenvalues. Now I have two main questions about this: 1. I know that if you apply a spin operator σ (which is...

Hello, Is it possible to build a qubit from an atom with a nuclear spin of zero (ie. 16O, 12C, 32S)? Would it depend on electron spin instead? Thanks!

Does spin for particles actually refer to spin as in rotation? Or does it mean something else. Do all elementary particles rotate? Without a magnetic field can you have rotation or does the rotation create the magnetic field?

Homework Statement When we use ##J^{/pm} ## where ##/pm## gives the parity, some sources say ##J## is the spin and some say the total angular momentum, I'm confused ! Also in my notes we have ##P=(-1)^l##, but looking on this thread...

Homework Statement Two identical spin-1/2 particles of mass m moving in one dimension have the Hamiltonian $$H=\frac{p_1^2}{2m} + \frac{p_2^2}{2m} + \frac{\lambda}{m}\delta(\mathbf r_1-\mathbf r_2)\mathbf s_1\cdot\mathbf s_2,$$ where (pi, ri, si) are the momentum, position, and spin operators...

I want to split a photon beam with no net angular momentum into two beams in both of which the sum of photon spins is not zero.

Suppose we define the total angular momentum as F = I+J where I is the nuclear spin angular momentum and J is the total electronic angular momentum. mF and mJ are the respective magnetic quantum numbers. The relevant F selection rules are delta_mF = 0, 1 and -1, delta_F = 0, 1 and -1. And...

In most introductory QFT treatments, it's stated early on (and without proof) that particles with even integral spin are always attractive, while those with odd integral spin can be repulsive; sometimes this is even cited as evidence that the graviton must be spin 2 (I think Feynman's...

Hi everyone! I am trying to create the density matrix for a spin-1/2 particle that is in thermal equilibrium at temperature T, and in a constant magnetic field oriented in the x-direction. This is a fairly straightforward process, but I'm getting stuck on one little part. Before starting I...

If the star's mass supposedly collapses into a single point, and it ends up having "said" zero volume, then how can people say that the hole has a specific spin or that it can have an angular momentum? Does it mean that the singularity is somehow still spinning, or maybe the spacetime around it...

Within the path integral framework, the reason you have to use Fadeev-Popov quantization for spin 1 is because the matrix of the coefficients of the quadratic part of the free-Lagrangian is non-invertible. But doesn't an i\epsilon prescription take care of that? The same thing happens with the...